What systems are backed up by the 747 tail auxiliary power engine?

747 Apu

1) First answer is correct. 2) I've never seen a camera in a toilet, I doubt there is one, but if there is, some kind of security function makes sense. 3) The second floor would probably be slightly safer than other parts of the airplane, but the most survivable places are in the very back, or over the front part of the wing. 4) There are numerous round things on airplanes, can you give more detail? 5) They turn off the lights and open the window shades for safety reasons... so rescuers can see in, and so your eyes can adjust to the dark... in case you need to get out of the airplane quickly.

On most transport category airplanes, the APU (Auxiliary Power UNIT) provides, as you said, power to the AC packs to keep cabin & cockpit temperatures comfortable while parked. It also provides electrical power to operate cabin equipment and cockpit instrumentation and provides 'bleed air' to start the main engines before pushback.

Since you asked what systems the APU backs-up of course the MES (Main Engine Start),Airconditioning & Pressurization System,Water & Waste system, Electrical system & Pneumatic system, both in flight and in ground: 25000ft only pneumatics and at 10000ft pneumatic and electrical can be supplied if an engine fails. The water & waste pressurization at initial aircraft start so you can have toilet flushing and potable water coming out of your lav and galley faucets and in flight is by differential pressure.

APU provides bleed air (air conditioning) and electrical power on the ground.

Bleed air also used for engine start.

APU can be used in-flight for some types airplane (optional).

747 APU

Sorry, wrong picture. this is the 747 APU - http://2.bp.blogspot.com/_XObgghPmt8g/TGsTbAf_owI/...